The present invention relates to an oil injection type hermetic scroll compressor for use as an air compressor, a helium compressor or the like.
Some types of hermetic scroll compressors having hermetic casings maintained in a high-pressure condition incorporate so-called oil injection systems in which an oil is injected for the purpose of cooling a compressed gas. In disclosed in, for example, Japanese Patent Unexamined Publication No. 61-112794 or U.S. Pat. No. 4,648,814, an oil injection system is generally arranged to effect separation of the oil injected into the compressed gas within the hermetic casing and store the resultant oil in a bottom portion of the hermetic casing. The oil injection system includes an oil extraction pipe for allowing injection of the oil into the compressed gas, with and one open end of the oil extraction pipe being located in the oil stored in the bottom portion, and an oil suction pipe is provided for supplying the oil as lubricating oil to the bearings of the compressor, with and one open end of the oil suction pipe located in the same stored oil.
A greater portion of the oil contained in the compressed gas is subjected to separation within the hermetic casing, and is stored in the bottom portion. The non-separated portion of the oil is fed to a discharge pipe of the compressor together with a discharged gas, and is subjected to separation in an oil separator disposed at a midway point in the discharge pipe. The thus-separated oil is injected into a suction pipe of the compressor or a compression chamber at an intermediate point of its compression stroke, so that the amount of oil stored in the bottom portion of the hermetic casing is maintained at a fixed level.
However, 1 problem of the above-proposed system resides in the fact that, in the event that no sufficient separation is accomplished by the oil separator disposed midway in the compressor discharge pipe, a portion of the oil will be discharged together with the compressed gas from the outlet side of the oil separator. As a result, the amount of oil stored in the bottom portion of the hermetic casing gradually decreases with the passage of time and, therefore, the amount of supply of a lubricating oil to the bearings of the compressor will decrease thereby possibly leading to the burning of the bearings.